In "Clues," the Enterprise apparently goes through a wormhole, which knocks out the entire ship, with the exception of Commander Data. In actuality, though, the wormhole is a ruse, a trick designed by the xenomorphic Paxans in order to keep their identity concealed from outsiders. Though the Enterprise crew is out for 24 hours, Data lies, insisting that the incapacitation only lasted for 30 seconds. Why does he lie? If he told the truth, then Dr. Crusher wouldn't have gone to Picard with her plants, she wouldn't have run a test on the last person to use the transporter, and Data wouldn't have had to use a weak excuse to try and defend his assertion that the crew was only out for 30 seconds. If he had told the bridge staff that the ship was out for 24 hours, and every piece of evidence showed this to be the case, Captain Picard might have believed the story Data told about the wormhole and continued forward, not bothering to go back and investigate. (And yes, I realize that without Data's lying, there likely wouldn't have been an episode, but I'm looking for in-universe reasons.)
Also, when the crew started getting suspicious and thinking that Data was up to something, why did Data not take Picard to the side and swear him to secrecy concerning the Paxans? Captain Picard is an honorable person, and I'm sure Data could have trusted him to keep his word. And yes, I know that Data promised to Picard never to reveal the Paxans' identity to anyone, but under the circumstances, and the likely destruction of the Enterprise, I think that Picard would have approved. Unless, somehow, the Paxans were able to monitor everything that Data said, but I don't think the episode shows this to be the case.